In a heated saucepan, bring pour the beef stock and bring it to a boil
Add the onions, garlic, soy sauce, Worcestershire sauce, brown sugar, salt, ground black pepper, and star anise to the beef stock.
Let the mixture simmer for 8 to 10 minutes and more water as needed.
Once the mixture has been brought to a simmer, turn off the heat and strain the mixture into a bowl.
Pour the strained mixture into a new heated saucepan and bring it to a boil.
Mix the cornstarch and water to create a diluted cornstarch mix
Add the cornstarch diluted in water then stir continuously until the texture becomes thick.
Turn off the heat and allow the mixture to cool down then transfer the Siopao sauce to a serving container.